(Bloomberg) -- NASA plans to replace an engine controller aboard its massive SLS rocket after finding a communications glitch with the system’s avionics during pre-flight testing, the latest setback for a Boeing Co.-led program plagued by years of delays and billions of dollars in costs beyond its initial budget.

The National Aeronautics and Space Administration also said Friday it will explore launch dates for a test flight in March and April.

The rocket, which Congress authorized and began funding in 2010, was supposed to fly in late 2016. In October, NASA solicited ideas from the aerospace industry about ways to lower the costs associated with the Space Launch System.

Replacing the unit on one of the SLS’s four RS-25 engines is “the best course of action,” the agency said. The update comes after engineers preparing the rocket for flight detected a communications problem last month between the rocket’s avionics system and the No. 4 engine, and began troubleshooting the issue.

NASA plans to use the Space Launch System rocket and Orion crew capsule to return astronauts to the moon later this decade. It had set a tentative launch date of Feb. 12 for the SLS-Orion system’s initial uncrewed Artemis 1 test flight around the moon.

Boeing is the rocket’s prime contractor and the RS-25 engines, which date to the Space Shuttle program, are supplied by Aerojet Rocketdyne Holdings Inc. The main contractor for the Orion crew capsule, which is designed to take astronauts to deep space, is Lockheed Martin Corp. 

For its initial four Artemis flights, NASA will likely spend $4.1 billion per launch for SLS and the Orion capsule, totaling $16.4 billion, according to a Nov. 15 NASA Inspector General report. The agency has spent more than $11 billion to date on the rocket. That document also predicted the first Artemis flight won’t be ready to launch before the summer of 2022.

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